An effective gene therapy for Parkinson's disease is the goal of this proposal, which will test the effectiveness and safety of human glial cell line derived neurotrophic factor (GDNF) delivered by two improved vector systems derived from equine infectious anemia virus (EIAV) or from adenoassociated virus (AAV). Both vectors deliver the cellular marker gene, nuclear localized lacZ (lacZnl) or GDNF efficiently and stably into nigrostriatal target regions, can be regulated using a tetracycline promoter system, and offer additional safety that the respective wild-type viruses do not cause any disease in humans. The recombinant vectors will be tested in the parkinsonian model produced by the neurotoxin MPTP in monkeys. GDNF has shown promise for preventing or reversing morphological, biochemical and functional deficits in other models of Parkinson's disease in rodents and primates, using rAAV, and rHIV. But these studies also showed important problems to be solved to ensure that a GDNF gene therapy will be safe and effective in patients. Concerns about inflammatory, cytotoxic, inadequate or excessive gene expression, persistence, viral recombination or replication have led to the development of improved and safer vectors with regulatable promoters, which will be tested in this proposed project. Initial studies will address transgene expression (lacZnl or GDNF) in normal African green monkeys, determining effective titers, transduction efficiency, cellular tropism, distribution, level, and stability of transgene expression, neuropathology and host cellular responses after delivery by rEIAV or rAAV. Each of the two vectors will then be used to deliver GDNF to the nigrostriatal system of MPTP parkinsonian monkeys to test hypotheses that GDNF expression will improve function in both moderate and severely parkinsonian monkeys for periods up to 24 months. The most effective procedures will be optimized by comparing injection sites, a regulatable promoter to inactivate gene expression, and safety of all procedures including high injection titers. Measures of efficacy will include behavioral parameters, molecular assays of transgene expression using ELISA for protein, RT-PCR for mRNA and PCR for vector DNA, biochemical assays of DA and its metabolites, neuroanatomical and morphometric analyses, neuropathology, clinical chemistry, SPECT imaging, and autoradiography. These studies aim to provide the necessary data to initiate successful clinical trials in Parkinson's patients at the earliest possible time.